# code: drawterm

View raw version
```#include "os.h"
#include <mp.h>
#include "dat.h"

#define LO(x) ((x) & ((1<<(Dbits/2))-1))
#define HI(x) ((x) >> (Dbits/2))

static void
mpdigmul(mpdigit a, mpdigit b, mpdigit *p)
{
mpdigit x, ah, al, bh, bl, p1, p2, p3, p4;
int carry;

// half digits
ah = HI(a);
al = LO(a);
bh = HI(b);
bl = LO(b);

// partial products
p1 = ah*bl;
p2 = bh*al;
p3 = bl*al;
p4 = ah*bh;

// p = ((p1+p2)<<(Dbits/2)) + (p4<<Dbits) + p3
carry = 0;
x = p1<<(Dbits/2);
p3 += x;
if(p3 < x)
carry++;
x = p2<<(Dbits/2);
p3 += x;
if(p3 < x)
carry++;
p4 += carry + HI(p1) + HI(p2);	// can't carry out of the high digit
p[0] = p3;
p[1] = p4;
}

// prereq: p must have room for n+1 digits
void
mpvecdigmuladd(mpdigit *b, int n, mpdigit m, mpdigit *p)
{
int i;
mpdigit carry, x, y, part[2];

carry = 0;
part[1] = 0;
for(i = 0; i < n; i++){
x = part[1] + carry;
if(x < carry)
carry = 1;
else
carry = 0;
y = *p;
mpdigmul(*b++, m, part);
x += part[0];
if(x < part[0])
carry++;
x += y;
if(x < y)
carry++;
*p++ = x;
}
*p = part[1] + carry;
}

// prereq: p must have room for n+1 digits
int
mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)
{
int i;
mpdigit x, y, part[2], borrow;

borrow = 0;
part[1] = 0;
for(i = 0; i < n; i++){
x = *p;
y = x - borrow;
if(y > x)
borrow = 1;
else
borrow = 0;
x = part[1];
mpdigmul(*b++, m, part);
x += part[0];
if(x < part[0])
borrow++;
x = y - x;
if(x > y)
borrow++;
*p++ = x;
}

x = *p;
y = x - borrow - part[1];
*p = y;
if(y > x)
return -1;
else
return 1;
}
```